A silicon (Si) based material is receiving a lot of attention as a negative electrode material for lithium ion battery.
Addition of a Si particle simple substance as a negative electrode active material, however, causes a large volume change (about 300%) as with inserting (intercalating)/separating of lithium ion. This involves progress of disintegrating of a Si particle, resulting in inviting a short cycle life. Further, due to mechanical disruption of Si negative electrode during an alloying/dealloying process thereof, immediate and irreversible reduction in an amount will occur, followed by lowering of coulombic efficiency.
A C—Si composite material is drawing an attention as a technology capable of solving the above described problem.
JP 2013-534024 A (Patent Literature 1) proposes: for example, “a combined hard carbon anode material for lithium ion battery characterized in that: a surface of a hard carbon substrate of the combined hard carbon anode material for lithium ion battery is covered with an encapsulated substance; and a precursor of the encapsulated substance is at least one of organic matters of epoxy resin, phenolic resin, carboxymethyl cellulose, pitch, ethyl methyl carbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, butadiene-styrene rubber, polyvinyl chloride, polyethylene, polyethylene oxide, polypropylene oxide, polyethylene succinate, polyethylene sebacate, polyethylene glycol imine, polyacetylene, polyparaphenylene, polyaniline, polypyrrole, polyacene, poly(m-phenylenediamine), polythiophene, poly(p-phenylene vinylene), polythiophene, polyacrylonitrile, polyimide, and polyphenylene sulfide, the organic matter/organic matters being pyroliytically decomposed to be formed into the encapsulated substance” and “a method for producing a combined hard carbon anode material for lithium ion battery including: Step 1 of obtaining a solid precursor by curing a thermoplastic resin for 3-50 hours at normal temperature in the air; Step 2 of obtaining powder having a particle size of 1-60 μm based on the precursor, at a nitrogen gas flow rate of 0.1-0.4 m3/hr., by raising a temperature of the precursor to 150° C.−450° C. at a rate of 0.1-3° C./min., presintering it at a low temperature for 2-24 hours, and naturally lowering the temperature thereof to the room temperature, followed by unraveling thereof; Step 3 of obtaining a hard carbon, at a nitrogen gas flow rate of 0.1-0.4 m3/min., by raising a temperature of the obtained powder to 560-1500° C. at a rate of 0.3-10° C./min., pyrolytically decomposing it for 0.5-7.5 hours, and naturally lowering the temperature thereof to the room temperature; Step 4 of obtaining a hard carbon substrate having a particle size of 1-60 μm by subjecting the obtained hard carbon to ball milling or pulverization; and Step 5 of obtaining a combined hard carbon anode material for lithium ion battery by adding a precursor of an encapsulated substance to the hard carbon substrate by an amount of 1-15 mass % of the precursor of the hard carbon substrate, mixing them at a rotation speed of 1400-3500 r/min. for 20-50 min., then, at a nitrogen gas flow rate of 0.1-0.4 m3/hr., raising a temperature thereof to 500-1500° C. at a rate of 1-7.5° C./min., pyrolytically decomposing the encapsulated substance for 2-8 hours, and naturally lowering the temperature thereof to the room temperature, wherein the thermoplastic resin is at least one of acrylic resin, polyvinyl chloride, polycarbonate, epoxy resin, phenolic resin, and polyformaldehyde; and wherein the precursor of the encapsulated substance is at least one organic matter of epoxy resin, phenolic resin, carboxymethyl cellulose, pitch, ethyl methyl carbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, butadiene-styrene rubber, polyvinyl chloride, polyethylene, polyethylene oxide, poly propane oxide, polyethylene succinate, polyethylene sebacate, polyethylene glycol imine, polyacetylene, polyparaphenylene, polyaniline, polypyrrole, polyacene, poly(m-phenylenediamine), polythiophene, poly(p-phenylene vinylene), polythiophene, polyacrylonitrile, polyimide, and polyphenylene sulfide”.
JP 2011-527982 A (Patent Literature 2) proposes: “a method for producing a conductive porous silicon and/or a tin-containing material to be used in producing an anode material for lithium ion battery, characterized in that: in a first processing step, a silicon nanoparticle and/or a tin nanoparticle and/or a silicon/tin nanoparticle is/are introduced into a matrix based on at least one polymer to be, specially, dispersed therein; and, in a second processing step, the polymer matrix containing the silicon nanoparticle and/or the tin nanoparticle and/or the silicon/tin nanoparticle is carbonized to be a carbon” and “the conductive porous silicon and/or tin-containing carbon material characterized in that the silicon and/or tin-containing carbon material contains a silicon nanoparticle and/or a tin nanoparticle and/or a silicon/tin nanoparticle in a porous carbon matrix, in the conductive porous silicon and/or the tin-containing carbon material, for producing the anode material for lithium ion battery.”